Samarium-153 ethylenediaminetetramethylene phosphonic acid ([153Sm]EDTMP) has been proposed to palliate pain resulting from osteoblastic metastatic bone cancer. Encouraging results in dogs with primary malignant bone cancer provided the catalysis for human biodistribution studies in five patients with metastatic skeletal carcinoma. The objective was to assess the preferential localization of [153Sm]EDTMP in bony lesions and compare it to the 99mTc-labeled phosphonates. Blood clearance of [153Sm]EDTMP was rapid with minimal accumulation in nonosseous tissues. Both radiopharmaceuticals showed identical lesion uptake in 23 paired lesions (p greater than 0.05). This indicates that the two radiopharmaceuticals concentrate in metastatic skeletal lesions by the same mechanism and since [153Sm]EDTMP emits beta radiation it may be therapeutically useful in ameliorating metastatic bony cancer pain.